This mod adds the number of currently owned resources to the tooltip when hovering either over the resource icon, or over the plot tile containing the resource.
The tooltip for the resource icon shows only a single number, which is the amount of resources currently available to you. It includes imported and exported resources, so it's the total amount of that type.
The tooltip for the plot tiles also includes this number, but additionally displays the amount of imported ("Im") and exported ("Ex") resources of this type. So the first number is still the total amount available to you right now.
Note: resources from being the Suzerain of a City States count towards the imported value.
Another note: I haven't made tests regarding performance, especially not in games with large/huge maps. Let me know if you encounter any performance issues.